Low prenatal serum 25-hydroxyvitamin D (25-OHD) concentrations are seen in infants born of mothers with decreased ultraviolet exposure (winter birth) and low postnatal serum 25-OHD concentrations are seen in premature infants dependent upon gestational age. Pathologic sequelae of these states of low serum 25-OHD concentrations have not been defined, however relationships have been suggested between a vitamin D deficiency and a) late neonatal hypocalcemia, b) early neonatal hypocalcemia, c) rickets in the premature, d) linear growth, e) developmental odontogenic disturbances and f) Sudden Infant Death Syndrome (SIDS). 100 term winterbirths, 100 healthy prematures of gestation less than 34 weeks, 35 infants of diabetic mothers, and 35 small-for-gestational-age infants will be followed prospectively from birth to 2 to 3 yrs of age to assess these possible correlations. 25-OHD2, 25-OHD3, calcium, magnesium and alkaline phosphatase will be determined for term infants in maternal sera, cord sera, 7 day sera and 3 month sera and for prematures, IDM's, and SGA infants in maternal, cord, 48 hr. 3 week, 6 week, and 3 month sera. A hand and wrist radiograph will be evaluated in premature infants at 3 weeks, 6 weeks, and 3 months and in term infants at 3 months. All infants will have dental examinations and dental radiographs at l year and at 2 to 3 years of age. In addition to the group to be followed prospectively, all cases of symptomatic early hypocalcemia, symptomatic late neonatal tetany, and SIDS will have serum 25-OHD2 and 25-OHD3 measured as well as other relevant determinations. It is hoped that definition of the clinical correlates of low 25-OHD2 and 25-OHD3 will provide a basis for the determination of optimal dosage and form of vitamin D requirements in high-risk groups of mothers and infants both prenatally and postnatally.